Conjugated diene polymers, on which many proposals have conventionally been made, are widely used, e.g., in tires, belts, impact modifiers for resins, pressure-sensitive adhesives, films and containers, mainly as elastomers, thermoplastic elastomers, and special transparent resins.
Typical known conjugated diene polymers include polybutadiene, polyisoprene, butadiene/isoprene copolymers, styrene/butadiene copolymers, styrene/isoprene copolymers, .alpha.-methylstyrene/butadiene copolymers, .alpha.-methylstyrene/isoprene copolymers, acrylonitrile/butadiene copolymers, acrylonitrile/isoprene copolymers, butadiene/methyl methacrylate copolymers, isoprene/methyl methacrylate copolymers, and hydrogenated polymers obtained therefrom.
On the other hand, block copolymers constituted of polymer blocks having a T.sub.g higher than room temperature (restrained phase) at both terminals thereof, and a polymer block having a T.sub.g lower than room temperature (rubbery phase) (e.g., styrene/butadiene (or isoprene)/styrene block copolymers and hydrogenated polymers obtained therefrom) interposed therebetween are widely used as thermoplastic elastomers, compatibilizing agents, and modifiers in many applications including injection molding and resin modification.
Blending of the styrene/butadiene (or isoprene)/styrene block copolymers or hydrogenated polymers obtained therefrom with other polymers, such as polystyrene, polyolefins, poly(phenylene ether), styrene/butadiene diblock copolymers, and hydrogenated polymers obtained from the diblock copolymers, to produce block copolymer compositions is widely conducted in order to improve the heat resistance, flowability, tackiness properties, and other properties of the styrene/butadiene (or isoprene)/styrene block copolymers or hydrogenated polymers obtained therefrom.
However, with the recent progress in technologies, the market demand for polymeric materials having even higher performances is becoming stronger, and there has been a strong desire for the development of a styrene-based thermoplastic elastomer having improved flowability and heat resistance. Although a styrene block copolymer having an improved balance between heat resistance and flowability has been obtainable, it has the following problems concerning moldability. When the styrene block copolymer is extrusion-molded into film, film breakage is apt to occur during film formation depending on molding conditions and the kind of the block copolymer, making stable film production impossible. Furthermore, when the styrene block copolymer is melt-blended with another resin and the blend is injection-molded, the resultant moldings have flow marks and hence a significantly impaired appearance. Consequently, there has been a strong desire for a styrene-based thermoplastic elastomer having an excellent balance among heat resistance, flowability and moldability.
One of the known effective means for meeting the above desire is to employ a radial block or to link a hydrogenated polybutadiene or hydrogenated polyisoprene block to an end of a styrene/hydrogenated polybutadiene (or hydrogenated polyisoprene)/styrene triblock polymer or of a similar triblock polymer to thereby improve the flowability of the block polymer. Another means is to blend a styrene/hydrogenated polybutadiene (or hydrogenated polyisoprene)/styrene triblock polymer or a similar triblock polymer with a styrene/hydrogenated polybutadiene (or hydrogenated polyisoprene) diblock polymer.
The present invention is based on a finding that a styrene/hydrogenated conjugated diene block copolymer upon melting, which is in a two-phase state (orderly state) consisting of a rubbery phase and a restrained phase, can be made to come into a single-phase state (disordered) at a lower temperature by regulating the block copolymer so as to contain a specific content of vinylaromatic hydrocarbon compound monomer units and a specific amount of a terminal hydrogenated conjugated diene block(s), and further based on a finding that due to the single-phase state (disorderly state) which the hydrogenated block copolymer undergoes, the copolymer alone or compositions containing the same can have even better moldability and excellent flowability and heat resistance.
Phase separation in molten block copolymers is described in Rheology Symposium Preprints, 43, p.169 (1995). It has been reported therein that styrene/hydrogenated polybutadiene/styrene block copolymers have various order-disorder transition temperatures depending on its styrene content and molecular weight. However, there is no description therein to the effect that order-disorder transition temperature is influenced by block arrangement, in particular that a block copolymer having a specific styrene content and containing a specific amount of terminal hydrogenated polybutadiene blocks has a considerably lowered order-disorder transition temperature. The present inventors have further found that hydrogenated block copolymers regulated to have a terminal hydrogenated conjugated diene block content not lower than 0.1% by weight and lower than 9.1% by weight, while maintaining the polystyrene chain length constant so as to have the same heat resistance, have a lowered order-disorder transition temperature and improved flowability, whereas hydrogenated block copolymers having a terminal hydrogenated conjugated diene block content out of the above range have an elevated order-disorder transition temperature or reduced flowability. As described above, regulating the content of vinylaromatic hydrocarbon compound monomer units to a value in a specific range and regulating the amount of terminal hydrogenated conjugated diene blocks to a value in the range of from 0.1 to 9.1%, excluding 9.1%, by weight are particularly important in the present invention from the standpoints of flowability, moldability, and heat resistance. It should however be noted that no report has so far been made on the fact that the presence of terminal hydrogenated conjugated diene blocks in a hydrogenated block copolymer in a specific amount as in the above range greatly improves the balance among flowability, heat resistance, and moldability of the copolymer.
Polyolefin resin compositions are widely used as mechanical parts, automotive parts, and the like because they are generally excellent in chemical resistance and mechanical properties. As a result of the recent trend toward size increase and wall thickness reduction in pursuit of functions and economy in various products, there is a desire for a polyolefin resin composition excellent in impact resistance, brittleness temperature, rigidity, surface hardness, and tensile elongation at break. In particular, tensile elongation at break is one of the highly desired properties. This is because polyolefin resin compositions, when used, for example, as an automotive material, are required not to break to scatter fragments upon impaction or required to deform to absorb impact, or because polyolefin resin compositions for use in the above applications are required not to break upon creep deformation.
A generally employed method for improving the impact resistance of polyolefin resins is to add an elastomer thereto. In Kobunshi Ronbun-shu, Vol.50, No.2, pp.81-86 (Feb. 1993) are shown various properties of compositions comprising polypropylene and an ethylene/propylene rubber as an elastomer. This report shows that increasing the addition amount of the elastomer improves impact resistance and tensile elongation at break. It is also shown therein that although reducing the molecular weight of the polypropylene so as to improve alloy flowability is effective in improving flowability, it reduces impact resistance and tensile elongation at break. In Kobunshi Ronbun-shu, Vol.50, No.1, pp.19-25 (Jan. 1993) is given a report showing that increasing the elastomer addition amount in compositions comprising polypropylene and an ethylene/propylene rubber impairs surface hardness.
Furthermore, many reports have conventionally been made on the addition of a hydrogenated block copolymer as a means for improving the impact resistance of polyolefin resins. In Plastic Age, Vol.42, p.117, Feb. (1996) are given results showing that in compositions comprising polypropylene and a hydrogenated block copolymer, increasing the addition amount of a hydrogenated styrene-based thermoplastic elastomer used as the hydrogenated block copolymer improves impact resistance but reduces rigidity. There also are results therein showing that although rigidity (flexural modulus) is improved by using an elastomer having a high styrene content, brittleness temperature is impaired thereby.
As apparent from the above, impact resistance, brittleness temperature, rigidity, surface hardness and tensile elongation at break are inconsistent with one another. It has hence been exceedingly difficult to obtain a highly improved balance among these properties.
In U.S. Pat. No. 4,168,286, there is claimed a hydrogenated block copolymer which has the structure of either a styrene/hydrogenated conjugated diene/styrene/hydrogenated polybutadiene block copolymer or a styrene/hydrogenated polybutadiene/styrene/hydrogenated conjugated diene block copolymer, and in which the 1,2-bond content in the hydrogenated polybutadiene block is from 1 to 10 mol %. However, in the hydrogenated block copolymers described in the Examples given in the above reference, the amount of the terminal hydrogenated polybutadiene block or terminal hydrogenated conjugated diene block is at least 20% by weight, which is outside the scope of the present invention. Moreover, in the above reference, there is no description nor suggestion concerning the effect of the amount of a terminal hydrogenated polybutadiene block or terminal hydrogenated conjugated diene block.
In JP-A-2-259151, there is claimed a stretchable nonwoven fabric comprising a styrene/hydrogenated polybutadiene/styrene/hydrogenated polybutadiene block copolymer. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) An Example given therein describes a styrene/hydrogenated polybutadiene/styrene/hydrogenated polybutadiene block copolymer in which the content of the terminal hydrogenated polybutadiene block is 10% by weight. However, this reference neither discloses a block copolymer having a terminal hydrogenated polybutadiene block in an amount below 10% by weight which is within the scope of the present invention, nor describes the effect thereof.
In JP-A-4-96904 and JP-A-4-96905, there is claimed a method for hydrogenating a styrene/butadiene block copolymer: An Example given in this reference describes a process in which a styrene/hydrogenated polybutadiene/styrene/hydrogenated polybutadiene block copolymer having a content of the terminal hydrogenated polybutadiene block of 10% by weight is produced.
In JP-A-5-038996, there is claimed an air bag cover housing comprising a hydrogenated conjugated diene block copolymer, a softener for rubber, and an olefin resin. An Example given in this reference describes an air bag housing material containing a styrene/hydrogenated polybutadiene/styrene/hydrogenated polybutadiene block copolymer in which the content of the terminal hydrogenated polybutadiene block is 10% by weight. However, the above two references each neither discloses a block copolymer having a terminal hydrogenated polybutadiene block in an amount smaller than 10% by weight, nor describes the effect thereof.
In JP-A-61-155446, there is claimed a composition comprising a hydrogenated block copolymer having a specific number-average molecular weight and a specific styrene content and having a specific amount of a hydrogenated polybutadiene block at the terminal thereof and a polyolefin. The Examples given therein describe compositions containing styrene/hydrogenated polybutadiene/styrene/hydrogenated polybutadiene block copolymers or hydrogenated polybutadiene/styrene/hydrogenated polybutadiene/styrene/hydrogenated polybutadiene block copolymers respectively having terminal hydrogenated polybutadiene block contents of 1.3, 2.5, 3, 5, 6.7, 10, 20, and 40% by weight. In the specification thereof, there is a description as to how the amount of the terminal hydrogenated polybutadiene block influences the mechanical strength and rubber elasticity of the composition. The composition claimed in this reference can have a styrene content of from 5 to 50% by weight, with the most preferred range thereof being from 10 to 40% by weight as described in the specification thereof. Although there is a description therein to the effect that the above range was employed in order to obtain desirable properties, there is no description nor suggestion therein concerning the relationship between the styrene content and a balance among impact resistance, brittleness temperature, rigidity, surface hardness and tensile elongation at break. Furthermore, the Examples given therein are limited to elastomer compositions having high elastomer contents, and no Example is given which relates to a resin composition showing a resin-modifying effect. In addition, there is no Example therein which relates to a composition produced by using a hydrogenated block copolymer containing a terminal hydrogenated polybutadiene block and having a vinylaromatic hydrocarbon content of 12% by weight or higher and lower than 25% by weight, which is one of the essential requirements in the present invention.
In Japanese Patent No. 2,500,391, there is claimed an elastomer composition which comprises a hydrogenated block copolymer having a hydrogenated polybutadiene block at an end, a polyolefin resin, and an ethylene/.alpha.-olefin copolymer, and which due to these components has the effect of being excellent in flexibility and processability and reduced in anisotropy. In this reference are given Examples concerning compositions containing a styrene/hydrogenated polybutadiene/styrene/hydrogenated polybutadiene block copolymer. In this reference, however, there is no description concerning the amount of the terminal hydrogenated polybutadiene block nor description suggesting the fact that the terminal hydrogenated polybutadiene block greatly improves the balance among impact resistance, brittleness temperature, rigidity, surface hardness and tensile elongation at break of the composition. In addition, the composition obtained according to this reference has an unsatisfactory balance among impact resistance, brittleness temperature, rigidity, surface hardness and tensile elongation at break.
Japanese Patent No. 2,529,807 discloses a composition obtained by compounding a polyolefin resin with a hydrogenated block copolymer and optionally further with an inorganic filler, for improving low-temperature impact strength and flowability/processability. In the Examples given therein are described compositions containing a hydrogenated block copolymer having the structure of polystyrene/hydrogenated polybutadiene (poly(ethylene-butylene)/polystyrene/hydrogenated polybutadiene. However, there is no description therein concerning an effect of the hydrogenated block copolymer used, although the vinyl content of the copolymer is shown. Furthermore, although the MFR, molecular weight, and styrene content of the hydrogenated block copolymer are shown in the above reference, there is no description therein concerning the relationship between these properties and tensile elongation at break. In addition, there is no description nor suggestion therein concerning the amount of a terminal hydrogenated polybutadiene chain and the effect thereof. Although this conventional technique is considerably effective in greatly improving flowability/processability, it is unsatisfactory in the improvement of tensile elongation at break.
JP-A-5-51494 discloses a composition comprising a polypropylene resin and two hydrogenated block copolymers having different molecular weights, for the purpose of improving low-temperature impact resistance, appearance properties and flowability/processability. In this reference are given Examples concerning compositions comprising a combination of a hydrogenated block copolymer having the structure of polystyrene/hydrogenated polybutadiene (poly(ethylene-butylene))/polystyrene/hydrogenated polybutadiene and a hydrogenated block copolymer having another structure. Although the influence of the microstructures of the conjugated diene compounds in the hydrogenated block copolymers used on low-temperature impact strength, rigidity and flowability/processability is shown in the above reference, there is no description therein concerning tensile elongation at break and surface hardness, and these two properties are not on a satisfactory level. In addition, there is no description nor suggestion therein concerning the amount of a terminal hydrogenated polybutadiene chain and the effect thereof.
JP-A-5-163388 discloses a composition which comprises a polypropylene resin and two hydrogenated block copolymers having different molecular weights and in which the hydrogenated block copolymer having a lower molecular weight is contained in a larger amount than the hydrogenated block copolymer having a higher molecular weight, for the purpose of improving the balance between low-temperature impact resistance and rigidity and improving flowability/processability. In this reference are given Examples concerning compositions containing a combination of hydrogenated block copolymers having the structure of polystyrene/hydrogenated polybutadiene (poly(ethylene-butylene)/polystyrene/hydrogenated polybutadiene and having different molecular weights. Although the influence of the microstructures of the conjugated diene compounds in the hydrogenated block copolymers used on low-temperature impact strength, rigidity, and flowability/processability is shown in the above reference, there is no description therein concerning tensile elongation at break and surface hardness and these two properties are not on a satisfactory level. In addition, there is no description nor suggestion therein concerning the amount of a terminal hydrogenated polybutadiene chain and an effect thereof.
JP-A-6-32947 discloses a composition obtained by compounding a polyolefin resin with a combination of hydrogenated block copolymers which differ in the microstructure of the conjugated diene block, for the purpose of improving the balance among practical low-temperature impact strength, heat deformation resistance and rigidity. In this reference are given Examples concerning compositions containing a combination of hydrogenated block copolymers having the structure of polystyrene/hydrogenated polybutadiene (poly(ethylene-butylene))/polystyrene/hydrogenated polybutadiene and differing in the microstructure of the conjugated diene block. Although the influence of the vinyl bond contents of the hydrogenated block copolymers used on impact strength, low-temperature impact strength and heat deformation resistance is shown in the above reference, there is no description therein concerning tensile elongation at break and surface hardness. In addition, there is no description nor suggestion concerning the amount of a terminal hydrogenated polybutadiene chain and an effect thereof. This conventional composition is not on a satisfactory level.
JP-A-7-188481 discloses a composition comprising a highly flowable polypropylene and a block copolymer having the structure of polystyrene/hydrogenated polyisoprene/polystyrene/hydrogenated polyisoprene, for the purpose of improving impact resistance, rigidity and heat deformation resistance. There is a description therein to the effect that by regulating the molecular weight of the terminal hydrogenated polyisoprene (so that the content thereof is from 9.17 to 23.1% by weight based on the whole block copolymer), the composition can be made to have excellent physical and appearance properties. Compositions in which the contents of the terminal hydrogenated polyisoprene block in the block copolymer are 11.7% by weight and 12.26% by weight are shown in Examples given in the above reference. However, not only the content of the terminal hydrogenated polyisoprene block in the block copolymer employed in this conventional composition is 9.17% by weight or higher, which is outside the scope of the present invention, but also there is no description therein concerning an effect which is produced when that content is lower than 9.17% by weight. Furthermore, there is no description in the above reference concerning the balance among impact resistance, brittleness temperature, rigidity, surface hardness and tensile elongation at break, and the conventional composition is unsatisfactory in that balance. In the Examples given therein are shown compositions employing a block copolymer obtained using isoprene as a conjugated diene compound. Although there is a description in the above reference to the effect that the isoprene block copolymer is more effective in property improvement than a butadiene block copolymer, there is no description nor suggestion concerning the relationship between MFR, microstructure, or the like and the effect of property improvement.
JP-A-8-20684 discloses a composition which comprises crystalline polypropylene and two hydrogenated block copolymers differing in melt flow rate (MFR) and in the content of a monovinyl-substituted aromatic hydrocarbon, and which is intended to be excellent in rigidity, heat deformation resistance and impact resistance and be satisfactory in appearance and moldability. There is a description therein to the effect that the composition tends to give moldings having flow marks and a poor appearance if the crystalline polypropylene has an MFR lower than 7 g/10 min or if one of the hydrogenated block copolymers has an MFR lower than 5 g/10 min. However, there is no description in the above reference concerning tensile elongation at break and surface hardness, and these properties of the conventional composition are not on a satisfactory level. Furthermore, there is no description nor suggestion therein concerning the amount of a terminal hydrogenated polybutadiene chain and the effect thereof.
JP-A-8-20690 discloses a composition obtained by compounding a polypropylene resin with polyethylene, an olefin elastomer, a hydrogenated block copolymer, and an inorganic filler, for the purpose of improving the balance among properties such as impact strength, injection moldability, rigidity, impact resistance and brittleness temperature. In this reference are given Examples concerning compositions containing a hydrogenated block copolymer having the structure of polystyrene/hydrogenated polybutadiene (poly(ethylene-butylene))/polystyrene/hydrogenated polybutadiene. Although the vinyl content of the hydrogenated block copolymer used is shown in the above reference, the effect thereof is not described. Furthermore, there is no description nor suggestion therein concerning the amount of a terminal hydrogenated polybutadiene chain and the effect thereof. This conventional technique is insufficient in the effect of improving hardness and tensile elongation at break, and a further improvement in this respect is desired.
As described above, a polyolefin resin composition has not yet been obtained which has an exceedingly good balance among impact resistance, brittleness temperature, rigidity, surface hardness and tensile elongation at break.